This invention relates in general to the distribution of conditioned air and more particularly to a pneumatic circuit which acts to control the discharge of conditioned air from ventilating ducts.
The heating and cooling of relatively large buildings such as office buildings is normally accomplished by passing conditioned air through ventilating ducts which direct the conditioned air to separate rooms of the building. Individual temperature control for the separate offices or other sections of the building is achieved by controlling the volume of air flow through the duct or through the air outlet which discharges the conditioned air from the duct into the room. Typically, a flow control device is provided in the duct or outlet to regulate the flow of conditioned air to an air diffuser or similar outlet device, thereby controlling the room temperature. This type of air distribution system is generally high in efficiency and low in cost since it utilizes a single large heating or cooling unit to supply several rooms or floors of the building. At the same time, there is no sacrifice in the individual temperature control for each office.
Despite its generally satisfactory performance, this type of air distribution system has not been entirely free of problems. For example, it has proven difficult to achieve accurate and repeatable control of the flow control device, and the temperature control of individual rooms has suffered accordingly. One of the main problems with this kind of air distribution system is that the flow from the outlets varies at least to some extent with the main supply pressure of the conditioned air. Thus, if the supply pressure increases, the air flow increases even though there is no increase in the demand for conditioned air.
Existing control systems devised to minimize this variation with supply pressure are characterized by excessive cost and complexity, due in large part to the need for a number of complicated components such as multiple diaphragms, associated springs, and the like. It is usually necessary, for control purposes, to provide a high velocity pressure or pressure differential on the high pressure side of the flow control device. This increases the need for pressure control components and adds to the fan requirements, thus contributing significantly to the high equipment and operating costs of the system.
The present invention is aimed at eliminating these problems and has, as its principal object, the provision of a pressure independent control circuit for controlling the discharge of conditioned air in an air distribution system. It is a particularly important feature of the invention that, for a given position of the thermostat, the air flow is determined by the pressure which is fed back from a velocity sensor located on the low pressure side of the duct outlet. The feedback signals from a velocity sensor thus automatically compensate for variations in the main supply pressure, and the control function of the circuit is not effected by pressure changes in the ventilation ducts.
It is another important object of the invention to provide a pneumatic control circuit which is simple and economical to construct and reliable in operation. Since only a single diaphragm is required to achieve pressure independent control, the costs are reduced as compared to control systems requiring numerous diaphragms and other pressure sensitive components.
A still further object of the invention is to provide a pneumatic control circuit of the character described which achieves accurate flow control without the need for a pressure differential on the high pressure side of the duct outlet. In the present invention, the pressure drop across the outlet is adequate for control purposes, and since this pressure drop is present in any event to assure effective air distribution, there is no need for the addition of a separate pressure or pressure differential for purposes of control. As a result, the complexity of the system and the fan requirements are reduced.
Yet another object of the invention is to provide, in a pneumatic control circuit of the character described, a plurality of strategically located and selectively sized orifices which assist in attaining the desired pressure and avoiding excessive pressure fluctuations.
An additional object of the invention is to provide, in a pneumatic control circuit of the character described, a pneumatic relay device which achieves both flow gain and pressure gain. A small orifice remote thermostat can thus control a relatively high flow rate to and from the bladder so that the control circuit responds quickly to changes in the demand for conditioned air. Also, a number of units operating at widely different supply pressures can be controlled by a single thermostat.
Another object of the invention is to provide a control which can be interlocked to a separate air system such that the controlled air system's flow varies inversely.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.